Tides: ebb and flow

In short: Tides are the regular rising and falling of sea level. They arise mainly from the gravitational pull of the Moon and, more weakly, the Sun.

In more detail: The Moon pulls the water on its side of the Earth. At the same time a second bulge forms on the far side. The Earth rotates through these bulges, so there is high water about twice a day.

In detail

• Rhythm: Between two high waters pass roughly 12 hours and 25 minutes.
• Spring tide: At full and new moon Sun and Moon act together, the tidal range is especially high (mondphasen).
• Neap tide: At half moon the difference between high and low water is small.
• Tidal range: On the North Sea about 2 to 4 metres, in the Bay of Fundy over 15 metres.
• Wadden Sea: At low tide the sea floor runs dry; mudflat hikes only with a guide.